1. Field of the Invention
The present invention relates to a well fluid additive, to a making a well fluid additive, to a well fluid, to a method of making a well fluid, to a method of treating well equipment, and to a method of drilling. In another aspect, the present invention relates to an oil-in-water emulsion drilling, completion or workover fluid additive, to a method of making an oil-in-water drilling, completion or workover fluid, to an oil-in-water drilling, completion or workover fluid, to a method of making such a fluid, and to a method of treating drilling, completion or workover equipment. In still yet another aspect, the present invention relates to oil-in-water well fluids and to treating methods utilizing a polyol having a cloud point such that uphole the polyol is soluble in the water phase, and downhole the polyol is soluble in the oil phase, effecting a cycle of emulsification and de-emulsification to provide larger lubricating oil droplets downhole.
2. Description of the Related Art
Hydrocarbons are found in subterranean formations and are produced through wells penetrating producing formations. Production of oil and gas is generally accomplished through the use of rotary drilling technology, which requires the drilling, completing and working over of wells.
The formation is composed of both inorganic and organic substances, such as clays and other minerals as well as fossils, peat etc. As the drill bit teeth penetrate the formation, drill chips are generated by the action of the bit. These drill chips are wetted by the drilling fluid which can produce sticky, plastic fragments. These fragments adhere to the bit surface and the force and weight of the bit extrudes the water from the plastic fragments forming a compacted mass of the formation onto the bit surface that interferes with the cutting action of the bit teeth as evidenced by a reduction in penetration rate. Balling also occurs on drill collars and stabilizers further interfering with drilling operations.
Bit balling resulting in the compaction and adherence of drill chips to the face of the cutters and the bit is a primary cause of reduction of penetration rate during drilling operations. Bit balling is believed to be the result of adhesive forces between shale and the bit surface which become significant when ductile shales deform and are forced into intimate contact with each other and the bit surface.
A liquid adheres to a solid surface if the attraction of the molecules to the solid surface is greater than their attraction to each other, i.e., the work of adhesion is greater than the work of cohesion. This criterion may be expressed thermodynamically as: EQU W.sub. =F.sub. +F.sub. -F.sub.
Where W.sub. is the work of adhesion; FS is the surface free energy of the solid; F.sub. is the surface free energy of the liquid; and F.sub. is the surface free energy of the newly formed interface. In terms of this expression, the work of cohesion, W.sub., is equal to xF.sub..
In order for adhesion to occur between the solid surface and a liquid, the work of adhesion must be greater than that of cohesion: EQU W.sub. -W.sub. =F.sub. -F.sub. -F.sub.
Accordingly, adhesion of the liquid to a solid occurs when the surface free energy of the solid surface exceeds that of the liquid and interface: EQU F.sub. &gt;F.sub. +F.sub.
Shales adhere to bits and drill collars if they are forced into intimate contact by the force and weight of the drill string. The mechanism of adhesion in this instance is probably hydrogen bonding extending from the molecular layers of water adsorbed on the shale surface to the layer of water adhering to the water-wet steel surface of the bit.
In the past, those skilled in the art have particularly relied upon use of oil-based or water-in-oil (invert emulsions) drilling fluids to eliminate or control bit balling, although several aqueous based fluids and additives have been contemplated by those skilled in the art. The environmental problems and costs associated with the use of oil-based or invert emulsion systems have discouraged and/or prohibited their use on many wells.
As for lubrication, it has been proposed to incorporate an emulsifier in water base drilling fluids where the lubricant utilized is insoluble in water.
U.S. Pat. No. 5,007,489, issued Apr. 16, 1991, and U.S. Pat. No. 5,099,930 issued Mar. 31, 1991, both to Enright et al, are both directed at overcoming the above described limitations of the prior art. Both of these patents disclose a method of lubricating well equipment and the prevention of balling of formation cuttings with the use of an additive comprising a non-water soluble polyglycol and an emulsifying surfactant.
While the additives of these Enright et al. patents are a remarkable improvement over the prior art, they, like the other prior art additives, are most effective at the time of their addition, with the effects of lubrication diminishing over time.
Without being limited by theory, applicants believe that with the prior art oil-in-water emulsion well fluids, the oil droplets in the emulsion are sheared into smaller and smaller droplets by the action of drill bit, as the drilling operation progresses over time. These smaller droplets are less effective in covering the drill bit and other metallic surfaces, resulting in direct contact of the water phase with the metallic surfaces causing bit balling and loss of lubrication.
Thus, there is still in need in the art for improved well fluid additives, methods of treating a well fluid, and method of treating a well.
These and other needs in the art will become apparent to those of skill in the art upon review of this patent specification, including its drawings and claims.